This invention relates to novel antimicrobial compositions of matter derived from naturally occurring flavanone glycosides and other plant phenolics. The present invention also relates to a novel process for preparing and isolating antimicrobial compositions of matter.
Over the years, many reports have appeared in the scientific literature claiming antimicrobial behavior for various natural plant phenolic compounds such as coumarin glycosides and flavanone glycosides. These various reports, however, have not been substantiated and have indeed been refuted by other workers. The antimicrobial properties of flavanoid glycosides, therefore, have remained a subject of controversy.
The broad class of chemical compounds known as flavanoid glycosides encompasses compounds including flavanone glycosides, coumarin glycosides and psoralin glycosides. Common examples of natural plant flavanoid glycosides include naringin, having the structure ##STR1## hesperidin, having the structure ##STR2## and esculin, having the structure ##STR3##
Natural plant flavanoid glycosides, which occur widely in nature, can be hydrolyzed in aqueous acid solution to yield such sugars as rhamnose and/or glucose and flavanoid aglycones. For example, hydrolysis of naringin, hesperidin, and esculin result in the formation, respectively, of the aglycones naringenin, which has the structure: ##STR4## hesperetin, which has the structure: ##STR5## esculetin, which has the structure: ##STR6##
In the prior art, the common practice has been to hydrolyze flavanoid glycosides in strong acid at a pH of 1 or less for several hours, accompanied by both vigorous stirring and heating at reaction temperatures approximating 100.degree. C. Under such conditions, the hydrolysis reaction proceeds to completion and generates flavanoid aglycones and sugars. It has been discovered, however, that if one uses dilute acid, quiescent conditions, and a limited reaction time, compositions having antimicrobial properties are obtained. In contrast, flavanoids do not possess antimicrobial properties.
The present invention permits the production of valuable antimicrobial compositions from naturally occuring plant material and clarifies the conflicting results reported in the literature with respect to the antimicrobial activity of phenolic glycosides. Specifically, the present invention teaches a process whereby one skilled in the art can easily and repeatedly convert natural flavanoid glycosides into isolable compositions of matter which have antimicrobial activity.